Smoke detectors are very commonly found today in buildings of all types. Some of these smoke detectors are AC powered. Others are battery powered. Some include a combination of AC power and battery backup power.
Battery powered detectors, while very convenient and easy to install, have suffered from the drawback that a user of the building might not realize the unit needed a battery. As such, because there was no indicia of a missing battery, this condition could persist for a substantial period of time to and including the time when a fire strikes the building. At that point in time, the detector would of course not function and not give out the warning it was intended to provide.
This problem has been dealt with in at least two different ways in the prior art. In a one known prior art detector the battery is located in a drawer which is radially movable with respect to the base.
So long as the battery is positioned in the drawer, the drawer can be freely opened and closed. When the drawer is closed with the battery present, the detector can receive electrical energy from the battery.
When the battery is removed from the drawer, the drawer is locked open and cannot be closed. This provides a visual indication of the missing battery.
While the drawer approach does provide an acceptable solution to the battery indicator problem from a consumer's point of view, from a manufacturer's point of view, it tends to be rather expensive and complicated.
An alternate prior art battery missing indicator has been incorporated into a smoke detector which is intended to be removably affixed to a surface mounted bracket. The bracket might be mounted on the ceiling or the wall of a room.
In this detector, when no battery is installed in the unit, a movable obstruction member extends out of a portion of the base which is intended to be located adjacent the bracket.
The presence of the extending obstruction is intended to make it impossible to couple the detector to the bracket. When a battery is inserted into the base of the detector, the obstructing member is depressed within the base of the detector by the battery. The detector can then be coupled to the bracket.
The above solution is of course not usable with detectors which are directly mountable on a surface without a bracket.
In spite of prior developments, there continues to be a need for cost-effective and reliable battery missing indicators which can be incorporated into electrical units such as battery powered smoke detectors. In addition, there continues to be a need for a simple apparatus of this type which readily conveys, visually, the missing battery indication to anybody passing through or in the area where the detector is mounted.